The present invention relates to a method of making a storage tank assembly, such as a fuel tank. The method includes the step of molding a container body over a portion of a plastic fixture to lock the fixture into the container body. The tank also includes easily installed components which can be easily mounted within the plastic fixture.
Traditionally, the fixtures in a plastic container such as a fuel tank are mounted to a metal plate. The metal plate provides a flat surface for a gasket which is used to prevent leakage of fuel from the tank. For example, the fixtures may be sandwiched between a pair of metal plates. The plates are bolted together with a gasket disposed between the plates to prevent leakage between the fixture and fuel tank. This requires placing a metal plate and screws inside the tank and on the outside of the tank. If the fixtures, gasket and metal plate are not properly aligned, leakage can occur around the screws and gasket.
Additionally, when plastic tanks expand due to pressure build-up within the tanks, they create a curved surface commonly called xe2x80x9ccrowningxe2x80x9d. Such crowning also affects the sealing ability of a gasket with respect to the tank. Fuel tanks which have undergone crowning provide poor sealing and fuel may leak out of the tank.
The prior art has not successfully addressed these problems. Thus, there has been a need for an improved plastic container assembly which provides improved high-pressure capacity using plastic fixtures without metal plates or gaskets. There has also been a need for an improved method of manufacturing these container assemblies.
The improved storage tank assembly of the present invention provides a fluid sealed tank without using gaskets or support plates which are typically used in plastic fuel tanks. The container assembly includes a plastic body and a plastic fixture. The plastic fixture has a first portion which defines an opening into the container body. A second portion of the plastic fixture includes at least one ridge on a surface of the fixture. The fixture surface and ridge are embedded in the container body and the ridge is deformed providing locking engagement between the fixture and the container body. When deformed, the cross section of the ridge is in the general form of a bead and the container body surrounds at least a portion of the bead to provide a positive lock between the fixture and the container.
In a method according to the present invention, a plastic container body is molded over a plastic fixture leaving a portion of the fixture partially embedded in the molded container body. A mold is provided having an inner surface and an orifice, wherein the inner surface defines an outer surface of the container body. A plastic fixture is disposed in the mold orifice with the fixture portion to be embedded in the container body positioned in the mold. The plastic fixture provides an opening into the molded container body. The plastic fixture also includes at least one ridge on a surface of the fixture which is to be embedded in the container body. A hot, fluid plastic material is introduced into the mold and forced against the mold inner surface and the surface of the fixture. The fluid plastic material softens or melts the ridge on the fixture. The ridge is deformed forming a locking engagement between the container body and the fixture. The ridge is further deformed due to the shrinkage of the fluid plastic material during cooling so as to form a bead which is at least partially surrounded by the plastic container body material. The plastic material also joins with the portion of the fixture embedded in the plastic container body. As a result, a container assembly is formed providing a secure seal between the container body and the plastic fixture. Thus, leakage which commonly occurs in plastic containers of this type is prevented even during crowning of the plastic container assembly.
In the disclosed embodiment, the ridges are initially triangular in cross-section. The molten plastic softens the triangular ridge and due to the force acting on the molten plastic, begins to force the apex of the ridge toward its base, flattening the apex and bulging the base into a generally bead shaped cross-section. As the molten plastic cools, it shrinks about the partially formed bead, further deforming the softened bead to engulf the bead within the cooling plastic to form a mechanical interlock. In cross-section, the deformed ridge has a bulbous head and narrow neck, all engulfed by the plastic of the container.
In the preferred embodiment, a roto-mold process is used to mold the tank. In this process, the molten plastic is introduced into the mold and the mold is rotated to force the plastic against the walls of the mold and against the plastic fixture. The plastic fixture is preferably made by an injection molding and same the same plastic composition as the container.
Another advantage of the fuel tank is that the gauges, inlets etc. are easier to fabricate and can have universal bases into which various components are inserted. This greatly reduces inventory and manufacturing costs.
These and other features of the present invention will be best understood from the following specification and drawings, of which the following is a brief description.